Many faucets have devices that control the temperature of the mixed output flow from hot and cold water supplies. One reason for thermostatic control is to eliminate constant readjustment of the valve when the temperature of the hot water supply fluctuates. The temperature of the hot water supply may vary substantially. The initial temperature of the hot water supply within the supply conduits may be cool after long periods of faucet inactivity particularly if the hot water tank is far from the faucet and the pipeline leading from the hot water tank to the faucet is long. Furthermore, if the hot water heater is being taxed to capacity and cannot keep up and the hot water tank is running out of hot water, the hot water supply may substantially cool down over a relatively short period of time.
Most known thermostatic faucet mixing valves work by changing the flow rates of both the hot and cold water simultaneously in opposite directions so as to keep the temperature of the mixed outlet water approximately constant within certain limits. The impetus of providing simultaneously lowering and increasing flow rates of the respective hot and cold water supplies and vice versa is to provide for a near constant flow rate during the thermostatic adjustments.
Many of these types of thermostatic mixing valves use the thermostatic element to determine a relatively narrow range of temperature allowed for the mixed outlet water and incorporate the thermostatic device into the mixing control. To adjust the temperature of the outflow, one adjusts the specialized mixing mechanism that incorporates the thermostatic element. Total flow rate then needs to be controlled by another mechanism. The inclusion of two separate mechanisms, one for controlling total flow rate and the other for controlling mix that incorporates the thermostatic element, adds needless expense and complexity to thermostatic faucets that lower their commercial desirability.
Another disadvantage of these known thermostatic devices becomes apparent when the hot water supply is received from an instantaneous hot water heater. Known instantaneous water heaters have a safety device that interrupts the heating in case the flow of water running through them becomes less than a certain predetermined limit. Known thermostatic control devices are able to reduce the flow rate from the hot water supply to below this limit, thus causing the water heater to shut off.
One known thermostatic device disclosed in German Patent 2,917,233 includes a thermostatic regulator that reduces the flow of the hot water supply when the temperature of the mixed water output exceeds a set value. In this case, due to the action of the thermostatic regulator, the flow of the cold and hot water supply is not simultaneously and oppositely controlled. Instead, while the hot water supply flow is controllably adjusted, the cold water flow remains relatively constant. However, when the hot water is supplied from an instant water heater, the same above mentioned disadvantage occurs.
What is needed is a thermostatic device that allows a standard mixing valve to function in both the flow rate and mixing mode while still providing a thermostatic control. Furthermore what is needed is a thermostatic device that does not cause deactivation of an instant water heater due to the thermostatic regulation on the water supplies such that the thermostatic faucet mixing valve is compatible with instant water heaters.